Furthermore, disease heterogeneity has not yet been studied in relation to recovery of muscle function in CFS. Here, we examine recovery of upper limb muscle function from a fatiguing exercise in CFS patients with (CFS+FM) and without (CFS-only) comorbid fibromyalgia and compare their results with a matched inactive control group.

RESULTS: There was no significant difference among the three groups for maximal handgrip strength of the non-dominant hand. A significant worse recovery of upper limb muscle function was found in the CFS+FM, but not in de CFS-only group compared with the controls (P < 0•05).

CONCLUSIONS: This study reveals, for the first time, delayed recovery of upper limb muscle function in CFS+FM, but not in CFS-only patients. The results underline that CFS is a heterogeneous disorder suggesting that reducing the heterogeneity of the disorder in future research is important to make progress towards a better understanding and uncovering of mechanisms regarding the nature of divers impairments in these patients.

I am awaiting the full report. This study is important as it separates two groups out biochemically based on self report. It also confirms what I have said for years that ME/CFS and FM are not different diseases but that the FM is a symptom of ME/CFS in some people genetically predisposed or traumatically predisposed (mainly spinal stenosis).

It may also tell something of the difference between the fatigue components, Some people having delayed muscle fibre recovery due to muscular mitochondrial dysfunction and accumulated lactic acid(the FM group) and those with centrally mediated fatigue which may be everyone with ME/CFS or another subset with ME/CFS.

Of course, notwithstanding those with "FM" who do not have fatigue (PEM) symptoms.

I see one key factor. The tested recovery time was initiated approximately one hour after the stress test. It is well known that in people with ME/CFS the worst effect of an exertion is felt on the second day. Can this muscular exertion can be compared with "body-wide" exertion? probably not. Body-wide exertion involves significant cardio-vascular changes which may account for P.E.M. So that people with ME/CFS (no FM) may recover quickly from a muscle stress test in the short term. Whether they suffer any kind of P.E.M many hours later (2 days) was not tested. Whereas the people with ME/CFS (+FM) recover slowly in the short term.

This is consistent with what we see clinically. People with FM suffer a lot of pain after muscle exertion and the muscular recovery time is slower than "normals". We have also found that resting muscle tension (fibre length) in FM is higher (fibres shorter) so that when they use the muscles concerned they are already more fatigued. I don't have enough data to comment on people with ME/CFS without FM.

So this is really a study of muscle recovery in FM. Even though this involves some exertion of the limb it is not exertion of the "whole body". This may produce different results too.

The authors also mention

Upper Limb Study

Posted by: caledoniaDec 26, 2013

I think the study was too small, and/or not designed to take PEM into account, and these differences would disappear in a larger or better designed study. I have ME/CFS only, yet I also have slower recovery in my upper limb muscles.